The present invention relates generally to the field of electric motors and wiring enclosures for housing the electrical connection between an external electrical power cable and internal electrical wiring of an electric motor. More particularly, the invention relates to a novel technique for securing a conduit box to an electric motor.
Electric motors of various types are omnipresent in industrial, commercial and consumer settings. In industry, such motors are employed to power all types of rotating machinery, such as pumps, conveyors, compressors, fans and so forth, to mention only a few. Conventional alternating current electric motors may be constructed for single or multiple phase operation, and are typically specifically designed to operate at predetermined synchronous speeds, such as 3600 rpm, 1800 rpm, 1200 rpm and so on. Such motors generally include a stator, comprising a multiplicity of coils, surrounding a rotor which is supported by bearings for rotation in the motor frame. In the case of AC motors, alternating current power applied to the motor causes the rotor to rotate within the stator at a speed which is a function of the frequency of alternating current input power and of the motor design (i.e., the number of poles defined by the motor windings and rotor resistance). In DC motors power is similarly applied, and the speed of the motor may be controlled in a variety of manners. In both cases, however, a rotor shaft extends through the motor housing and is connected to elements of the machinery driven by the electric motor.
In conventional electric motors, stator winding coils are disposed in parallel slots formed around the inner periphery of a stator core. Certain of the winding coils are electrically connected in groups around the stator core to establish the desired electro-magnetic fields used to induce rotation of the rotor. The number and locations of the windings in the stator core generally depends upon the design of the motor (e.g., the number of poles, the number of stator slots, the number of winding groups, and so forth). Each winding coil includes a number of turns of wire that loop around end or head regions of the stator between the slots in which the winding coil is installed. Following installation in the slots, the coils in each group are generally pressed into a bundle at either end of the stator. The stator windings are connected to electrical wiring that is routed from the stator to a wiring or conduit box located on the outside of the motor through corresponding holes in the motor frame and the conduit box.
The conduit box enables an external power cable to be connected to the electrical wiring coupled to the stator windings without having to access the interior of the motor housing. The conduit box, typically, has a removable cover to enable unimpeded access to the wiring within the conduit box. In general, a conduit box is a housing that is configured to receive a length of electrical conduit housing a power cable. The power cable is routed through a hole in the conduit box into the interior of the conduit box. The conductors of the power cable and the electrical wiring from the motor stator are spliced together and the cable splice is placed in the interior of the conduit box. The cover is then secured to the conduit box and other facets of motor installation may be completed.
While conventional conduit boxes and motor arrangements have been generally satisfactory in may applications, they are not without drawbacks. For example, conduit boxes are typically secured to the motor via screws installed through the box wall and into the motor frame. To provide a seal between the conduit box and motor frame, a grommet is typically placed in the hole between the conduit box and the motor frame to prevent chafing of the wiring passing through the hole. Multiple screws are typically used to secure the conduit box to the motor frame. The resulting structure is relatively complex, includes a number of separate parts, and, in a typical procedure, is assembled by hand. Despite attempts to protect the wiring at the location where it passes through the motor frame and conduit box, damage and even short circuits can occur. Moreover, the cost of the assembly can be considerable as compared to the overall cost of the motor, particularly for smaller or fractional horsepower models.
There is a need, therefore, for an improved technique for securing a conduit box to an electric motor. There is a particular need for a technique that provides a more straightforward structure from a manufacturing and assembly standpoint and that therefore offers possible cost reductions. The technique should notably provide effective prevention of chafing of the wiring passing through the conduit box, while offering a satisfactory seal between the box and the motor frame.
The invention provides a novel approach to securing a conduit box to an electric motor designed to respond to these needs. The technique can be employed in various motor configurations, including AC and DC motors, and motors configured with 2, 4, 6 or more poles, for single or multiple phase operation, and from fractional horsepower""s to very large power ratings. The technique is based on the plastic deformation of a portion of the conduit box.
In accordance with the first aspect of the technique, a method is provided for manufacturing an electric motor. The method utilizes a novel technique for securing a conduit box to an electric motor. A conduit box is adapted to have a hollow extension. The hollow extension is placed on the motor housing to place the extension through a hole in the motor housing. A tool is pressed against the extension to enlarge the width of the extension so that it is greater than the diameter of the hole in the motor housing, preventing the conduit box from being removed from the hole.
In accordance with another aspect of the technique, an electric motor is provided that has a conduit box secured thereto. The conduit box has a portion that extends through a hole in the motor frame. The portion that extends through the motor frame is plastically deformed to secure the conduit box to the motor frame.